Differential thermostat.



PATENTED AUG. 18, 1908.

' W. H. CARRIER.

DIFFERENTIAL THERMOSTAT.

APPLICATION FILED 0O T.l1, 1907.

UNITED STATES PATENT orrion.

WILLIS H. CARRIER, OF BUFFALO, NEW YORK, ASSIGNOR TO BUFFALO FORGECOMPANY,

OF BUFFALO, NEW YORK.

DIFFERENTIAL THERMOST A'I.

Specification of Letters Patent.

Patented Aug. 18, 1908.

Application filed October 11, 1907. Serial No. 396,983.

Toall whom it may concern:

Be it known that I, WILLIS H. CARRIER, a citizen of the United States,residing at Buffalo, in the county of Erie and State of New York, haveinvented a new and useful Improvement in Differential Thermostats, ofwhich the following is a specification.

This invention relates to a differential thermostat which is influencedby the temperature and hygrometric' condition of the atmospheresurrounding it, and it is utilized primarily for regulating the relativehumidity of the air in factories or elsewhere.

The thermostat operates upon the principle of the psychrometer, or wetbulb hygrom eter, '5. 6., it has an element, corresponding to the drybulbof the psychrometer, which is affected directly by the temperatureof the surrounding air and another element which is insulated from thefirst and is subjected to the lower temperature roduced by theevaporation of a moist bo y in its immediate vicinity. The moist bodyevaporates more rapidly in proportion as the air is drier and thetemperature of the body sinks in consequence of this evaporation. Thetwo elements of the thermostat are consequently influenced respectivelyby the different dry and wet bulb temperatures of the air and willexpand or contract differentially so that the osition of a device 0erated by their conoint action will depenc upon the relation existingbetween the temperature and humidity of the air. Preferably thethermostat elements act differentially on a device by artthe thermostatis locate can be increased or decreased to secure a desired relativehumidity. If the coefficients of expansion of the two'thermostatelements bear a fixed relation, the instrument will 0 erate inaccordance with a constant'wet bu b depression which would give anincreasing relative humidity with a rise of temperature, but

ment in which the device is preferably provi ed with adjusting meanswhereby it is possible to vary the ratio of expansion of its elements tocorrespond to the ratio existing between the variations in the wet bulbdepressions and the variations in dry bulb temperatures within theprescribed range and thus obtain an approximately constant percentage ofrelative humidity for any given range of temperatures. As anillustration, suppose that sult can be obtained by using theconstruction shown in t a constant relative humidity of 60 per cent. isdesired for temperatures ranging between 70 and 85 F. The psychrometrictables show that for 60 er cent. relative humidity at 70, the wet Bulbtemperature must be 615, a depression of 8?, while for the same humidityat 85 the wet bulb temperature must be 74?, or a depression of 10%? Thusfor this range there will be a rise of 15 in the dry bulb temperature,and a rise of only 13? in the ,wet bulb temperature. This ratio ofincrease in the dry and wet bulb tem eratures is approximately the samefor al dry bulb temperatures between 70 and 85, so that for a constantrelative humidity of 60% it will be necessary for the thermostat to haveelements whose coefficients of expansion bear the ratio of 15 to 13; 'i.e., such that for every 13 units the dry bulb element expands, the wetbulb element will expand 15 units. This retwo dissimilar metals havinga'ratio of expansion of 13 to 15, but as the ratio differs for differentrelative humidities in different -ranges of temperature, adjusting meansare provided, as before mentioned, for changing at will the ratio of exansion of the two elements.

11 the accompanying drawings: Figure 1 is a central sectional elevationof a differential thermostat embodying the invention. Fig. 2 is asectional elevation of the upper portion thereof in line 22, Fig. 1. 1Fig. 3 is a sectional plan in line 3-3, Fig. 1.

Like letters of reference refer to like parts in the several figures.

The thermostatcomprises two expansible elements A and B which areinsulated from each other, one element being secured at one end andinfluenced by the temperature of the surrounding atmosphere, and theother element being connected to the free end of the first element andinfluenced by a lower temperature caused by the eva oration of moisturefrom a body or wick 0 suitable absorbent material C surroundin the same.In e drawings, one element B is arranged concentrically within the otherelement A, which latter is tubular and perforated and is secured at itsup er end to a hollow box or casing D. A cap E is secured to and closesthe lower end of the outer element, and the inner element is se cured atits lower end to and is supported by this cap. If a single-piece innerelement having a fixed coeflicient of expansion were used it could besecured to the cap E in any suitable manner, but preferably it has ascrew connection with .an adjusting screw F the element B and turmng theadjusting screw one way or the other it will be screwed farther into orout of the element and the effective expa'nsible length of the partswill be changed without shifting the element B lengthwise. Thus by usingmetals having different coefficients of expansion for the parts B and F,which in reality together form the inner element, it is ossible to alterits coeflicient of expansion y screwing the adjusting'screw farther intoor out of the art .B. A stem or shaft f extends through a ole in the topof the casing D and has an end of square 'or other suitable shapeloosely engag ing in a corresponding hole-1n the upper end of the innerelement, so that the latter can be heldor turned by means of the shaft,while the shaft does not interfere-with the free' ex-' pansion andcontraction of the element. By olding the adjustin screw F and turningthe element B thereon by the shaft f, the position of the elementrelative to the art actuated thereby canbe adjusted as requlred. The twoelements are suitably insulated from each other to prevent thecommunication of the temperature of one to the other, for which pur osea flange g on the lower end of the inner e ement is embraced by acoupling ring g screwed on the cap E, and suitable insulating material 9is provided between the flanged end of the inner element and the cap Eand coupling ring g. A suitable insulating ring 9 1s also placed betweenthe body and top of the casing D to further complete the insulation ofthe two elements. I A pipe H connects the casing D with an exhauster ofany suitable sort whereby an upward current of air is produced withinthe outer element around the inner element, the air entering through theperforations inthe outer element. A tube I secured to the casing D anddepending into the outer element around the inner element nearly to thelower end thereof, insures an upward draft or current in'proximity tothe inner element for the greater part of its length, and also serves tov that surrounding and influencing the outer' element.

partially insulateorseparate' the air immeiately surrounding the innerelement from i The wick or absorbent body 0 surrounding the innerelement extends from the lower end of the inner element approximately tothe upper end thereof, and then laterally and up t ough a tube 7cpassing through the top of the casing D into a reservoir or receptacle Kfor water-or other suitable liquid for wetting thejwick, the upper endof the wick being preferably immersed in the liquid in the reservoir K.The reservoir is supplied with liquid, preferably by apetcock k whichdrips thereinto. ,The reservoir is preferably provided with anoverflow'passage orpipej ,2 ocated at an elevation slightly above thetop of the wick tube 7: so that the level ofthe liquid will bemaintained above the upper end of the wick tube to give a constantslighthead or pressure to the liquid, which assists the c'apillaryaction ofthe wick in keeping the same thoroughly wetted at all times. The cap Eis also preferably provided with an overflow or drain passage or pipe 7:above the lower end of the wick, so that a body of liquid is maintainedin the cap into which the lower end of the wick dips.

L represents a lever which is fulcrumed in the stationary casing D bypivots Z, or in any other suitable manner, and is providedwith anopening through which the shaft f for the upper'end of the inner elementpasses. A plug l fixed to the upper end of the inner element is providedat opposite sides with knife edges on which the lever L bears. Thethermostat lever L can be connected to suitable means whereby thethermostat can be em loye'dfor indicating the relative humld ty of t eatmosphere in the apartment in WhlCh it is located, or for contro lingthe humidity of the air. e As shown, the lever is connected to anordinary thermostatic valve, indicated at M, which controls the supplyof compressed air in a passage m m leading to means (not shown) forhumidifying or dehumidifying the air in the apartment in which thethermostat is located.

The 0 eration of the thermostat is as follows: T e wick 0 around theinner element BF is kept wet and the air 'circulated upwardly around thesame evaporates the moisture and lowers the temperature of the innerelementaccording to the humidity of. the air, and the ratio of expansionof the two thermostat elements, depending upon the humidity of the air,will determine the position of the lever L and consequently the actionof the humidity regulating means con trolled thereby. By means of theadj usting screw F the ratio of expansion of the elements can be alteredto give a constant wet bulb depression with a varying relative humiditywith chan esin temperature, or a varying wet bulb epression such as togive an ape proximately'constant relative humidity with fluctuations oftemperature for the reason before explained.

:AI claim as my invention:

'1. The combination of a thermostat elementinfluenced by the temperatureof the surrounding air, a second thermostat element insulated from saidfirst element, means whereby moisture is evaporated in the vicinity ofsaid second element, and mechanical surrounding air, a second'thermostatelement insulated from said first element but mechanically connectedthereto, and a molst body enveloping said second element whereby itstemperature corresponds substantially to the wet bulb temperature of theair, said elements having different coefficients of. expansion,substantially as set forth.

3. The combination of a thermostat element influenced by the temperatureof the surrounding air, a second thermostat ele ment insulated from saidfirst element but mechanically connected thereto, a moist bodyenveloping said second element, and means for producing an air currentpast sald moist body, substantially as set forth.

4. The combination of a hollow thermostat element influenced by thesurrounding air, a second thermostat element arranged within andinsulated from said hollow element but mechanically connected thereto, amoist body enveloping said inner element, and means whereby the air canmove in said hollow element around said moist body, substantially as setforth.

5. The combination of a hollow thermostat element having an air inletand adapted for connection with means for causing the passage of airtherethrough, a second thermostat element arranged within" and insulatedfrom said hollow element but mechanically connected thereto, and a moistbody envelo ing saidinner element, substantially as set orth. Y

6. The combination of a hollow perforated thermostat element havingmeans for connection with an air exhauster, a second thermostat elementlocated within and insulated from but mechanically connected to saidhollow element, a moist body enveloping said inner element, and a tubewithin said outer element and surrounding said inner element stantiallyas set forth.

to form an air passage around the same, substantially as set forth.

7. The combination of a thermostat element influenced bythe temperatureof the surrounding air, a' second thermostat element insulated from butmechanically connected to said first element, means whereby moisture isevaporated in the vicinity of said second element, and means forchanging the ratio of expansion of said elements, substantially as setforth. 3

8. The combination of a thermostat element influencedby the temperatureof the surrounding air, a second thermostat ele-' ment insulated frombut mechanically con nected to said first element, one of said elementscomprising parts having different coefficients of expansion which areadjustably connected for relatively changingthe effective expansiblelengths of said parts, and means whereby moisture is evaporated in thevicinity of said-second element, sub- 9. The combinatlon of a hollowthermostatelement influenced by the surrounding air, a second thermostatelement arranged Within and insulated from said hollow element, anadjusting device which has a different coefficient of expansion fromsaid inner element and has screw connections with both'of said elements,and a moist body envelo in said inner element, substantially as set011%}.

10. The combination of a hollow thermostat element influenced by thesurrounding air,. a second thermostat element ar ranged within andinsulated from said hollow element but mechanically connected thereto, awick envelo ing said inner element, a reservoir into w ich the upper endof said wick extends, and means for maintaining liquid in said reservoirat a predetermined level for wetting said wick, substantially as setforth.

Witness my hand, this7th day of October, 1907.

WILLIS H. CARRIER. Witnesses:

O. W. PARKER,

C. B. HORNBECK.

